This invention relates to injection timing control systems for fuel-injection pumps for engines, and more particularly to an injection timing control system for a fuel-injection pump of an engine in which a phase angle regulator is provided for varying the rotational phase angle of a drive shaft of the fuel-injection pump, the regulator having an input shaft adapted to be driven by the engine and an output shaft for driving the drive shaft of the fuel-injection pump.
Heretofore, in order to increase the engine operating efficiency and to effect exhaust emission control of an internal combustion engine, such as a diesel engine, it has been customary to vary the fuel-injection timing in a fuel-injection pump used for the engine in accordance with the change of the engine speed.
Systems for varying the fuel-injection timing in fuel-injection pumps can be broadly divided into two types. One of such types detects the engine speed by means of a centrifugal type governor and causes the rotational phase angle of a drive shaft of the fuel-injection pump to vary based on the detected value. The other type detects the engine speed and the drive rotational phase angle of the fuel-injection pump independently of each other and inputs the detection signals to a computer which outputs an electric signal corresponding to a rotational phase angle of the drive shaft which best suits the engine operating condition including engine speed, the output signal of the computer being converted into hydraulic power for rendering a hydraulic actuator operative, so as to cause the hydraulic actuator to effect control of the rotational phase angle of the drive shaft of the fuel-injection pump through a link mechanism.
In the aforesaid systems of the prior art, the first system using a governor has a difficulty in increasing the response speed in effecting control thereof because of its having a non-linear characteristic. The second system is basically capable of having a superb control characteristic because the detection signals each have a linear characteristic. However, since it uses a link mechanism through which a hydraulic actuator controls the rotational phase angle of the drive shaft of the fuel-injection pump as a final step, the second system is faced with the problems that mechanical play is produced in the link mechanism after its prolonged use and this causes deterioration of its control characteristic, and that it is impossible to obtain an overall compact size of the system. Also, the arrangement whereby the detection mechanisms for the engine speed and the rotational phase angle of the drive shaft of the fuel-injection pump are provided independently is a factor concerned in the inability to obtain an overall compact size of the system. It is important to obtain an overall compact size of the system, since if the overall size of the system is not compact, then it is impossible to mount the system snugly in the narrow engine room and no small difficulty is encountered in installing the system.